1. Field of the Invention
This invention concerns a soil or ground quality stabilizer produced by mixing a highly pure fine iron oxide powder byproduced in steel production, a burned sewage sludge ash byproduced at municipal sewage disposal plants and a highly pure slaked lime together and a treatment method of adding the soil or ground quality stabilizer into a soil or ground and mixing together to enhance the strength and viscoelasticity of the soil or ground.
2. Description of the Prior Art
The total length of paved roads would be approximately 770,000 km or about 70% of the total roads of 1,110,000 km and the roads paved with asphalt concrete (a pavement to make the surface with asphalt concrete) would be above 95% of the paved roads in Japan. The shear strength of the asphalt concrete can be maintained by keeping the air voids of the mixture at a specified percentage (3-7%). However, the viscosity resistance of asphalt is greatly dependent on the temperature and as the resistance falls during the hot summer, the asphalt concrete would be tightened by heavy traffic loads to decrease the air voids percentage.
When the air voids percentage falls below 2%, the shear strength would sharply drop and a fluid rutting occurs to lose the pavement function. However, should the air voids percentage of the asphalt concrete be larger than the specified percentage, the asphalt in the mixture would react with oxygen and be hardened to lose the viscosity and a crack destruction would occur due to a lack of flexibility during the cold winter.
Japan is a long and slender chain of islands extending from the north to the south and because of its topographical features of sharp difference in the altitudes, the climatic conditions are such rigorous one to the asphalt pavement as heavy snow in the northern Japan and in the mountains during winter and the rise in the temperature up to 60.degree. C. at the surface of the asphalt concrete with 30.degree. C. of ambient temperature in summer. Further the traffic conditions are such that the registered heavy vehicles in Japan are about 10 times more than those registered in a major country in Europe and a larger destructive action is being given to the pavement in Japan. For this reason the paved roads are designed to be durable for ten years in Japan.
Nevertheless, the heavy traffic roads are apt to cause fluid ruttings due to the insufficient strength in hot summer and relatively less heavy traffic roads lose the pavement function due to a crack destruction caused by the insufficient flexibility through an aging of the asphalt.
As a result, such heavy traffic roads in general area are obliged to be repaired in 3-4 years after the service was started, since the fluid rutting reaches the serviceable limit. Such counter-measures for the fluid rutting as an improvement of the thermal sensitivity of the asphalt are being taken but there were other problems like a crack that occurred frequently and sufficient measures have not yet been established. The method of adding lime has been used to stabilize or reinforce a soil or ground for many years and the reaction mechanism is (1) to make a lump of the soil particles through an ion-exchange reaction on the particle surface and (2) to give a hardening action through the formation of calcium carbonate. However, according to recent research, (3) noncrystalline substances such as silica( SiO.sub.2) or alumina (Al.sub.2 O.sub.3) which forms the clay or colloids in the soil or ground would hydrate with lime in the soil or ground to produce calcium silicate hydrate or calcium aluminate hydrate. These materials in a single form or in a composit form can serve as a binder to increase the strength and to maintain the durability.
In general, this reaction is called Pozzolan Reaction and the success of a soil or ground quality stabilizing with lime is considered to be dependent on the Pozzolan Reaction.
In case a soil or ground quality stabilizing material made from natural soil added with lime or cement is used as a pavement construction material, the strength and the viscoelasticity are in the relationship of antinomy each other.
For instance, it was impossible to obtain the properties having above 1.0% strain at the maximum stress and above 10 Kg/cm.sup.2 of the single axis compression strength simultaneously.
Now such properties have become obtainable by using a soil or ground quality stabilizing material made from a Fe oxides mixture added with lime and the purpose intended was achieved tentatively. The soil or ground quality stabilizing material which is a blend of a fine Fe oxides powder and slaked lime or quick lime or lime stone powder shall be called "Fe lime" in this specification hereafter.
The inventors of this application have made some inventions based on this Fe lime with acceptable achievements so far.
For instance, the inventions are on a paved road construction method by making the soft base of subgrade intermediate course with a mixture of natural soil, converter slag, a fine iron oxide powder and slaked lime (please refer to Japan Patent Publication No. 52-7256), and on a simplified road pavement construction method by providing a reinforced soil or ground material course as an intermediate course in between the base material course and the subgrade to utilize the chemical reaction of natural soil added with a fine iron oxide powder and slaked lime (please refer to Japan Patent Publication No. 54-25738) and further on a prevention method of settlement due to consolidation by reinforcing the soft base by making the surface ground with a reinforced soil or ground material made from natural soil added with a fine iron oxide powder and slaked lime and by making the thickness of the reinforced soil or ground material course the one that can secure an elastic coefficient below the critical deflection against the load of constructed structure (Japan Patent Application Laid Open No. 63-134709).
The Fe lime process is to replace a part of the ground subgrade with the treated soil of pavement materials containing soil added and mixed with the Fe lime. This process does not require much rolling pressure for compression hardening and a relatively uniform strength is obtainable and for this reason the process is recognized as Sandwitch process.
This process can reduce the pavement thickness remarkably and give a fairly longer service life as compared with the process of replacing with a good soil. The structural dynamic analysis of this mechanism has not yet been made but it is considered that the improved viscoelasticity of the soil or ground strata treated with the Fe lime works as a cushion against traffic loads. It is further considered that such characteristics may be obtained through a combined reaction between the conventional stabilizing reaction by the lime and a conditional change in the iron of the fine iron oxide powder caused by the coexistance with the slaked lime (Magazine [Pavement] 28-6, 1993 by Yorimasa Abe et al).
The Fe lime containing the fine iron oxide powder and the slaked lime is also mixed with red mud containing Ti oxide to produce a soil or ground reinforcing material which is added into a pavement material containing crushed stones, natural soil, etc. (U.S. Pat. No. 5,456,553).
The soil or ground stabilizing treatment using the Fe lime is able to produce a fairly good quality material because in case the soil in which the Fe lime is to be mixed (the soil used) is a decomposed granite which is a remained soil of weathered granite rock, it contains much reactive noncrystalline materials (such as SiO.sub.2, Al.sub.2 O.sub.3 and Fe.sub.2 O.sub.3).
However, if the soil used is a high crystalline material consisting of SiO.sub.2 which is represented by silica sand such as a hill sand, riverbed earth and sand and gravel soil containing less clay or unweathered pyroelastic flow deposit the main mineral of which is volcanic glass and most of the contents are sand and silt called sirsu, there is such a problem that the soil contains little noncrystalline material and therefore the strength intended cannot be obtained.
The object of this invention is to present a new soil or ground quality stabilizer and a treatment method thereof that can give the strength and viscoelasticity intended to each course in the pavement by making the soil or ground quality stabilizer of a specific composition without limiting to a specific soil to be used. The soil or ground quality stablizer according to the present invention and the treatment method can improve the strength greatly without impairing the deflection property of the conventional stabilized or reinforced soil or ground material with the Fe lime. Hence, an application of this invention to the base upper course of a heavy traffic road has become possible and the deflection of a pavement can be substantially reduced and such a structural destruction of the pavement and a fluid rutting can be prevented by the buffer action of the viscoelasticity as well.
Another object of this invention is to provide a stabilizing method of a soil or ground quality that can give a specified California Bearing Ratio (CBR) or other industry standard strength to the soil or ground having an increased moisture therein.